A GSM network comprises a Base Station Subsystem (BSS) and a Network and Switching Subsystem (NSS). It can also comprise other parts, such as a GPRS core network. The Base Station Subsystem (BSS) is responsible for handling traffic and signaling between mobile units and the Network Switching Subsystem (NSS). The BSS carries out for example transcoding of speech channels, allocation of radio channels to mobile units, paging, quality management of transmission and reception over an Air interface (Um) to the mobile stations. The Network Switching Subsystem (NSS) is also referred to as the GSM core network. It is arranged to carry out switching functions and management of communications between mobile stations and the Public Switched Telephone Network (PSTN).
In GSM networks, operators may share BSS equipment.
U.S. Pat. No. 7,236,784 relates to selecting a public land mobile network (PLMN) from a plurality of available PLMNs. In this disclosure, the mobile stations of a radio network are arranged to select one PLMN from the plurality of available PLMNs.
Further, Inter PLMN (Public Land Mobile Network) handover is not standardized in 3GPP. However, PLMN handovers are still used and works well in several commercial mobile telephony networks.